1. Field of the Invention
The present invention relates to a fuel cell system, more specifically, relates to a fuel cell system preventing leakage of inner liquid and reducing the number of pumps so as to be compactly constituted.
2. Description of the Related Art
In general, a fuel cell is provided with an anode 3, a cathode 5 and an electrolyte film 7 put therebetween as shown in FIG. 1, in which a direct methanol fuel cell is exemplified. FIG. 2 shows an example of a fuel cell system considered to be a general constitution thereof. Fuel (methanol in this case) is supplied to the anode 3 by mean of a pump 11 and gas (generally air) which contains oxidant (generally oxygen) is supplied to the cathode 5 by means of a pump 13. At the anode 3 and the cathode 5, following reactions respectively progress.
At the anode 3;CH3OH+H2O→CO2+6H++6e−−121.9 kJ/mol  (1)
At the cathode 5;3/2O2+6H++6e−−>3H2O+141.95 kJ/mol  (2)
If the protons and the electrons are freely transported between the anode 3 and the cathode 5, net reaction as described below is completed in the fuel cell. Thereby an electric power generation can not be achieved.CH3OH+3/2O2−>CO2+2H2O+20.05 kJ/mol  (3)
However, the electrolyte film 7 has a cation selectivity so that cations (protons in this case) are selectively transported therethrough in preference to anions (electrons in this case). Therefore the electrons are extracted from the fuel cell so that the electric power generation is made possible as shown in FIG. 1. In the course of the power generation, carbon dioxide is generated at the anode 3 and water is generated at the cathode 5.
To develop the cation selectivity, it is necessary to humidify the electrolyte film 7 with water. It is proposed that the water is admixed to the methanol in advance so as to be supplied to the electrolyte film 7.
It is known that the methanol partly percolates the electrolyte film 7 from the anode 3 to the cathode 5 and such methanol is called “crossover methanol”. The crossover methanol reacts with water according to the reaction equation (1) at the cathode 5 and causes a counter electromotive force so that the power generation of the fuel cell is suppressed.
A related art is disclosed in Japanese Patent Application Laid-open No. 2002-110199. In the fuel cell system of the related art, the reaction products in the anode and/or the cathode are recycled.